Light Emitting Diodes (LEDs) have many advantages over conventional light sources, such as incandescent, halogen and fluorescent lamps. These advantages include longer operating life, lower power consumption, and smaller size. Consequently, conventional light sources are increasingly being replaced with LEDs in traditional lighting applications. As an example, LEDs are currently being used in flashlights, camera flashes, traffic signal lights, automotive taillights and display devices. LEDs have also gained favor in residential, industrial, and retail lighting applications.
Color temperature is a simplified way to characterize the spectral properties of a light source. While in reality the color of light is determined by how much each point on the spectral curve contributes to its output, the result can still be summarized on a linear scale. This value is useful, for example, for specifying the right light source types in architectural lighting design. Note, however, that light sources of the same color (metamers) can vary widely in the quality of light emitted. One may have a continuous spectrum, while the other just emits light in a few narrow bands of the spectrum. A useful way to determine the quality of a light source is its color rendering index. The Correlated Color Temperature (CCT) is a specification of the color appearance of the light emitted by a light source, relating its color to the color of light from a reference source when heated to a particular temperature, measured in degrees Kelvin (K).
Low color temperature implies warmer (more yellow/red) light while high color temperature implies a colder (more blue) light. Daylight has a rather low color temperature near dawn, and a higher one during the day.
Existing LED lighting exhibits color shift during dimming. Said another way, when the amount of current provided to an LED or group of LEDs is reduced from one current value to another current value, the brightness of the LED will change, but so too will the color produced by the LED. When the current provided to an LED is reduced from the maximum input current to the minimum allowable input current, the color of the LED could shift by as much as 300K CCT, which is generally noticeable by users. Because of this color-shifting phenomenon, it has been more difficult to provide a suitable LED alternative for dimmable lights.